Rare-earth oxide sintered body and manufacturing method

ABSTRACT

A rare-earth oxide sintered body, or corrosion-resistant material, having low sintering temperature and high density is prepared by adding a boron compound at a ratio of 0.06 mol % or more and less than 25 mol % when converted into boron oxide (B 2 O 3 ) to oxide powder of at least one of La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Sc, after which the mixed powder is formed and sintered. The sintered body comprises at least one of La 2 O 3 , Nd 2 O 3 , Sm 2 O 3 , Eu 2 O 3 , Gd 2 O 3 , Dy 2 O 3 , Ho 2 O 3 , Er 2 O 3 , Tm 2 O 3 , Yb 2 O 3 , Lu 2 O 3 , and Sc 2 O 3 , and at least one of Ln 3 BO 6  (Ln=La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu), and Sc 3 BO 6  as a main constituent crystal thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. Ser. No. 11/487,956, filed 17 Jul. 2006, which claims priority from Japanese patent application 2005-277123, filed 26 Sep. 2005, and Japanese patent application 2006-192343, filed 13 Jul. 2006. The entire disclosure of each of the referenced priority documents is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method in which a rare-earth oxide can be sintered at low temperature.

2. Description of Background Art

As a common ceramic, alumina (Al₂O₃) or zirconia (ZrO₂) have been used. Although there is known amorphous formation, single-crystal growth and thin-film formation as the formation method, sintering is the most common method. Also, in order to easily complete sintering, a sintering aid is used.

The present inventors have paid attention to boron oxide (B₂O₃) as a sintering aid. Patent Document 1 and Non-patent Document 1 can be listed as a background art material in which boron oxide (B₂O₃) is used as a sintering aid.

Patent Document 1, Japanese Patent Application Publication No. 2000-239065, has disclosed that yttria (Y₂O₃) powder is formed by cold isostatical press (CIP), the formed body is fired at 1400-1800° C., cooled, and thereafter heated at 1400-2000° C. in the presence of a boron compound (B₂O₃), so that a dense yttria (Y₂O₃) sintered body can be obtained. According to Patent Document 1, it is assumed that the dense sintered body can be obtained because the presence of a boron compound promotes sintering due to diffusion of B₂O₃ inside the body.

Non-patent Document 1, Production of Transparent Yttrium Oxide by HIP sintering, The Ceramic Society of Japan, 2004, Preprint 2G09, has disclosed that yttria (Y₂O₃) powder is formed by CIP (140 MPa), first sintering is performed to the formed body at 1400-1700° C., BN is sprayed on the sintered body, and second sintering is performed by HIP (140 MPa, 1400-1700° C.), so that an yttria (Y₂O₃) sintered body having excellent transparency can be obtained.

However, according to these documents, firing at relatively high temperature such as 1700-2000° C. is required to obtain a sintered body having small porosity, or a complicated manufacturing process such as HIP processing after first sintering is required to obtain a sintered body.

An object of the present invention is to provide a rare-earth oxide sintered body and a corrosion-resistance material having high density and excellent plasma-resistance which can be manufactured easily at low temperature, and a manufacturing method thereof.

SUMMARY OF THE INVENTION

The above prior art materials fail to describe that boron oxide (B₂O₃) is added to rare-earth oxide powder as a sintering aid. Therefore, the present inventors made experiments on La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Sc among rare-earth elements.

As a result, it was confirmed that addition of boron oxide (B₂O₃) is effective with respect to rare-earth oxides of La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Sc.

Therefore, the rare-earth oxide sintered body according to the present invention includes at least one of Ln₃BO₆ (Ln=La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu), and Sc₃BO₆, together with at least one of the corresponding rare-earth oxides (La₂O₃, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃, and Sc₂O₃) as a main constituent crystal thereof.

The above-described rare-earth oxide sintered body includes a compound of rare earth and boron in which at least one of Ln₃BO₆ and Sc₃BO₆ includes as a main constituent crystal of the sintered body, so that the relative density of the sintered body can be increased. Incidentally, Ln refers to La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, or Lu.

Further, in order to allow the sintered body to include a compound of rare earth and boron as Ln₃BO₆ or Sc₃BO₆ so as to increase the relative density, the addition ratio of the boron oxide (B₂O₃) to the rare-earth oxide is 0.06 mol % or more and less than 25 mol %.

Each rare-earth element has different sintering temperature, and an element having a smaller ion radius tends to need higher sintering temperature. For example, the sintering temperature is 1100-1300° C. when boron oxide (B₂O₃) is added to lanthanum oxide (La₂O₃) (3 wt %:12.6 mol %), the sintering temperature is 1200-1400° C. when boron oxide (B₂O₃) is added to samarium oxide (Sm₂O₃) (3 wt %:13.4 mol %), the sintering temperature is 1100-1300° C. when boron oxide (B₂O₃) is added to neodymium oxide (Nd₂O₃) (3 wt %:13.0 mol %), and the sintering temperature is 1400-1500° C. when boron oxide (B₂O₃) is added to ytterbium oxide (Yb₂O₃) (3 wt %:14.9 mol %).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to lanthanum oxide (La₂O₃) powder;

FIG. 2 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to samarium oxide (Sm₂O₃) powder;

FIG. 3 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to neodymium oxide (Nd₂O₃) powder;

FIG. 4 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to ytterbium oxide (Yb₂O₃) powder;

FIG. 5 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to europium oxide (Eu₂O₃) powder;

FIG. 6 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to dysprosium oxide (Dy₂O₃) powder;

FIG. 7 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to gadolinium oxide (Gd₂O₃) powder;

FIG. 8 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to holmium oxide (Ho₂O₃) powder;

FIG. 9 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to erbium oxide (Er₂O₃) powder;

FIG. 10 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to scandium oxide (Sc₂O₃) powder;

FIG. 11 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to thulium oxide (Tm₂O₃) powder; and

FIG. 12 is a graph showing the relationship between firing temperature and relative density when boron oxide (B₂O₃) powder is added to lutetium oxide (Lu₂O₃) powder.

DETAILED DESCRIPTION OF PRESENT EMBODIMENTS Example 1

Lanthanum oxide (La₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to lanthanum oxide (La₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to lanthanum oxide (La₂O₃) powder at a ratio of 3.0 wt % (12.6 mol %) were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 1. FIG. 1 shows that the relative density is around 80% in the case of adding no boron oxide (B₂O₃), while the relative density exceeds 95% at around 1130° C. and the sintering completes around 1200° C. where the relative density is around 99% or more in the case of adding boron oxide (B₂O₃) to lanthanum oxide (La₂O₃).

Example 2

Samarium oxide (Sm₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to samarium oxide (Sm₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to samarium oxide (Sm₂O₃) powder at a ratio of 3.0 wt % (13.4 mol %) were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 2. FIG. 2 shows that the relative density exceeds 95% at around 1200° C. and the sintering completes around 1300° C. where the relative density is around 99% or more in the case of adding boron oxide (B₂O₃) to samarium oxide (Sm₂O₃).

Example 3

Neodymium oxide (Nd₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to neodymium oxide (Nd₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to neodymium oxide (Nd₂O₃) powder at a ratio of 3.0 wt % (13.0 mol %) were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 3. FIG. 3 shows that the sintering completes around 1200° C. where the relative density is around 95% or more in the case of adding boron oxide (B₂O₃) to neodymium oxide (Nd₂O₃).

Example 4

Ytterbium oxide (Yb₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to ytterbium oxide (Yb₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to ytterbium oxide (Yb₂O₃) powder at a ratio of 3.0 wt % (14.9 mol %) were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 4. FIG. 4 shows that the relative density is around 60-70% in the case of adding no boron oxide (B₂O₃), while the relative density exceeds 95% at around 1500° C. in the case of adding boron oxide (B₂O₃) to ytterbium oxide (Yb₂O₃).

Example 5

Europium oxide (Eu₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to europium oxide (Eu₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to europium oxide (Eu₂O₃) powder at a ratio of 9.0 mol % were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 5. FIG. 5 shows that densification occurs at 1300° C. or more in the case of adding no boron oxide (B₂O₃), while the relative density exceeds 95% at around 1200° C. and the sintering completes at around 1300° C. where the relative density is around 99% or more in the case of adding boron oxide (B₂O₃) to europium oxide (Eu₂O₃).

Example 6

Dysprosium oxide (Dy₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to dysprosium oxide (Dy₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to dysprosium oxide (Dy₂O₃) powder at a ratio of 9.0 mol % were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 6. FIG. 6 shows the relative density is around 95% in the case of adding no boron oxide (B₂O₃), while the relative density exceeds around 99% at 1300-1400° C. in the case of adding boron oxide (B₂O₃) to dysprosium oxide (Dy₂O₃) powder.

Example 7

Gadolinium oxide (Gd₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to gadolinium oxide (Gd₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to gadolinium oxide (Gd₂O₃) powder at a ratio of 9.0 mol % were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 7. FIG. 7 shows that densification occurs at 1500° C. or more in the case of adding no boron oxide (B₂O₃), while the relative density exceeds 99% at around 1300° C. and the sintering completes at around 1300-1400° C. where the relative density is around 99% or more in the case of adding boron oxide (B₂O₃) to gadolinium oxide (Gd₂O₃).

Example 8

Holmium oxide (Ho₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to holmium oxide (Ho₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to holmium oxide (Ho₂O₃) powder at a ratio of 9.0 mol % were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 8. FIG. 8 shows that the firing curve has a similar tendency in the case of adding no boron oxide (B₂O₃) and the case of adding boron oxide (B₂O₃) to holmium oxide (Ho₂O₃). However, densification further proceeds in the case of adding boron oxide (B₂O₃).

Example 9

Erbium oxide (Er₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to erbium oxide (Er₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to erbium oxide (Er₂O₃) powder at a ratio of 9.0 mol % were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 9. FIG. 9 shows that densification occurs at 1700° C. in the case of adding no boron oxide (B₂O₃), while the relative density exceeds 95% at around 1400° C. and the sintering completes at around 1500° C. where the relative density is around 99% or more in the case of adding boron oxide (B₂O₃) to erbium oxide (Er₂O₃).

Example 10

Scandium oxide (Sc₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to scandium oxide (Sc₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to scandium oxide (Sc₂O₃) powder at a ratio of 9.0 mol % were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 10. FIG. 10 shows that the firing curve has a similar tendency in the case of adding no boron oxide (B₂O₃) and the case of adding boron oxide (B₂O₃) to scandium oxide (Sc₂O₃). However, densification further proceeds in the case of adding boron oxide (B₂O₃).

Example 11

Thulium oxide (Tm₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to thulium oxide (Tm₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to thulium oxide (Tm₂O₃) powder at a ratio of 9.0 mol % were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 11. FIG. 11 shows that the relative density exceeds 80% at 1700° C. in the case of adding no boron oxide (B₂O₃), while the relative density exceeds 90% at around 1500° C. and a sintered body having high density can be obtained at around 1500° C. in the case of adding boron oxide (B₂O₃) to thulium oxide (Tm₂O₃).

Example 12

Lutetium oxide (Lu₂O₃) powder and boron oxide (B₂O₃) powder were prepared as raw powders. A sample in which boron oxide (B₂O₃) powder was not added to lutetium oxide (Lu₂O₃) powder and another sample in which boron oxide (B₂O₃) powder was added to lutetium oxide (Lu₂O₃) powder at a ratio of 9.0 mol % were prepared. The two kinds of samples were formed and fired at a firing furnace.

The relationship between the firing temperature and the relative density is shown in FIG. 12. FIG. 12 shows that the relative density is less than 80% at 1700° C. in the case of adding no boron oxide (B₂O₃), while the relative density is around 90% at around 1500° C. and a sintered body having high density can be obtained at around 1600° C. in the case of adding boron oxide (B₂O₃) to lutetium oxide (Lu₂O₃).

According to the present invention, it is possible to obtain a sintered body having density of 95% at relatively low temperature less than 1550° C.

When the temperature is less than 1550° C., it is possible to perform firing easily in an atmosphere with a general-purpose firing furnace using a molybdenum disilicide heater or an SiC heater as a heating member.

As the boron compound, boric acid (H₃BO₃), boron nitride (BN) or boron carbide (B₄C) may be used as well as boron oxide. Among these, boron oxide and boric acid are preferred.

Also, plasma-resistance was evaluated. The evaluation method is as follows: Samples were polished such that each sintered body had a surface roughness (Ra) of 0.1 μm or less. Half the surface of each sample was masked, and irradiated with plasma by using CF₄+O₂ as etching gas at 1000 W for 30 hours in an RIE plasma etching apparatus. After irradiation, the mask was removed, and the difference between the masked area and non-masked area were measured so as to calculate the etching speed (nm/hr). The results are shown in Table 1. In the examples, boron oxide (B₂O₃) of 9 mol % was added to rare-earth oxides. In the comparative example, high-purity alumina (purity: 99.7%) was used. Table 1 shows that rare-earth oxides to which boron oxide (B₂O₃) was added as a sintering aid had much lower etching speed and better plasma-resistance than high-purity alumina.

TABLE 1 Etching speed Material (nm/hr) Example Eu₂O₃ 70 Gd₂O₃ 93 Dy₂O₃ 53 Ho₂O₃ 47 Er₂O₃ 50 Tm₂O₃ 47 Yb₂O₃ 43 Lu₂O₃ 43 Sc₂O₃ 27 Comparative Al₂O₃ 217 Example

The rare-earth oxide sintered body according to the present invention can be used as a corrosion-resistant material which requires plasma-resistance such as a chamber, a capture ring, a focus ring, an electrostatic chuck of a plasma processing apparatus.

According to the present invention, it is possible to obtain a rare-earth oxide sintered body having high density at relatively low temperature.

Although there have been described what are the present embodiments of the invention, it will be understood that variations and modifications may be made thereto within the scope of the claims appended hereto. 

1. A method for manufacturing a rare-earth oxide sintered body comprising the steps of: adding a boron compound at a ratio of 0.06 mol % or more and less than 25 mol % when converted into boron oxide (B₂O₃) to oxide powder of at least one of La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, and Sc; forming the mixed powder; and performing sintering such that a resulting sintered body comprises at least one of La₂O₃, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃, and Sc₂O₃, and at least one of Ln₃BO₆ (Ln=La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu), and Sc₃BO₆ as a main constituent crystal thereof.
 2. A method according to claim 1, wherein the sintering is performed at a temperature of at least 1100° C.
 3. A method according to claim 1, wherein the sintered body comprises Ln₃BO₆ (Ln=La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu) and at least one of La₂O₃, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃ as the main constituent crystal thereof and is sintered at a temperature in a range of approximately 1100° C.-1550° C.
 4. A method according to claim 1, wherein the sintered body comprises at least one of Lu₃BO₆, Yb₃BO₆, Tm₃BO₆, and Sc₃BO₆, and at least one of Lu₂O₃, Yb₂O₃, Tm₂O₃, and Sc₂O₃ as the main constituent crystal thereof and is sintered at a temperature in a range of approximately 1100° C.-1700° C.
 5. A method according to claim 1, consisting essentially of at least one of La₂O₃, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃, and Sc₂O₃, and at least one of Ln₃BO₆ (Ln=La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu), and Sc₃BO₆. 